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mySingle-Storey Extension Cost
At a Glance
- The average cost of building a single-storey extension in the UK is £35,000, or around £1,700 per square metre.
- Most single-storey extensions take around 12 weeks to complete.
- NEW! Try our single-storey extension cost calculator for an instant estimate.
- Typical costs for single-storey extensions by size, type, and finish.
- How long projects take and what will drive the extension costs you're quoted up.
- How to find a local builder with MyJobQuote.
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£35,000
Table of Contents
- How Much Does a Single-Storey Extension Cost in the UK?
- Single-Storey Extension Costs by Type
- Labour Cost of a Single-Storey Extension
- Supply Cost of a Single-Storey Extension
- Additional Single-Storey Extension Costs
- What Impacts the Cost of a Single-Storey Extension?
- Single-Storey Extension Roof Costs
- Benefits of a Single-Storey Extension
- Building Regulations & Planning Permission for a Single-Storey Extension
- What's Involved in Building a Single-Storey Extension?
- Single-Storey Extension Alternatives
- Checklist: Hiring a Single-Storey Extension Builder in the UK
- FAQs
How Much Does a Single-Storey Extension Cost in the UK?
The average cost of a single-storey extension is around £35,000. This would give you a good-sized rear or side extension with basic materials and include the cost of a kitchen (which is a common use for a single-storey extension).
By comparison, the cost of a two-storey extension is typically around £60,000.
A single-storey extension is a popular type of home extension in the UK and single-storey extension costs will vary depending on the size of the extension and the quality of materials you choose.
The average cost of a single-storey extension per square metre (m²) in the UK is around £1,700.
This means a small, basic single-storey extension of 5 to 10m² can cost as little as £15,000, and a large, high-quality 50m² single-storey extension could cost up to £100,000.
Single-Storey Extension Price List
With all costs included, the quality of the finish is one of the most significant factors affecting the single-storey extension cost.
This table highlights how the price range differs between an extension that uses basic, good, or high-end materials:
| Quality of Finish | Average Cost (20m²) | Cost per m² |
|---|---|---|
| Basic | £27,000 | £1,000–£1,700 |
| Good | £36,000 | £1,700–£1,900 |
| High | £41,000 | £1,900–£2,200 |
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But, what can you expect the ground floor extension cost to be for different-sized extensions?
We've collected together what you should expect in the table below:
| Size of Single-Storey Extension | Average Cost | Average Cost Range |
|---|---|---|
| 20m² (Small) | £30,000 | £20,000–£44,000 |
| 30m² (Medium) | £48,000 | £30,000–£66,000 |
| 50m² (Large) | £80,000 | £50,000–£110,000 |
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To get a more accurate estimate for your build, try our single-storey extension cost calculator below!
Single-Storey Extension Cost Calculator
Single-Storey Extension Costs by Type
There are five main types of single-storey extensions that homeowners in the UK typically have:
| Type of Extension | Typical Size | Average Cost |
|---|---|---|
| Side Return Extension | 5m² to 10m² | £15,000–£20,000 |
| Side Extension | 15m² to 20m² | £30,000 |
| Rear Extension | 15m² to 20m² | £30,000–£40,000 |
| Wraparound Extension | 30m² to 40m² | £50,000–£100,000 |
| Kitchen Extension | 15m² to 20m² | £50,000 |
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In this section, we've covered the average prices quoted for each of these, as well as the pros and cons of each option.
What is your main reason for a single-storey extension?
Creating additional living space
18 votes - 51%51% of votes
Adding extra bedrooms, bathrooms, etc
12 votes - 34%34% of votes
Making the property larger without needing to move
2 votes - 6%6% of votes
To increase the value of your property
3 votes - 9%9% of votes
35 votes
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Single-Storey Side Return Extension Cost
A side return extension uses the alleyways that run down the sides of some houses. Many Victorian houses have these little alleyways, which are often used to store bins.
Single-storey side return extension costs in the UK are around £15,000 to £20,000, or from £2,000 per m².
Pros
- ✔ Quick to complete.
- ✔ Doesn't use garden space.
Cons
- ✖ Only creates a small amount of extra living space.
- ✖ Not an option for all houses.
Single-Storey Side Extension Cost
A side extension makes use of the space to the side of your property, to create a single-storey extension that can be used for a variety of purposes.
The average single-storey side extension cost in the UK is around £30,000, or £1,700 per m².
Pros
- ✔ Creates more usable living space.
- ✔ Doesn't reduce rear garden space.
Cons
- ✖ May reduce access to the rear garden.
- ✖ Not an option for all houses.
Single-Storey Rear Extension Cost
Rear extensions are usually just a single room-sized extension to the rear of a property, so they are a good choice if you only want a small extension. A lean-to is one common form of rear extension, with a single-slope roof that leans against the existing wall.
The average single-storey rear extension cost in the UK is between £30,000 and £40,000, or £1,800 per m².
Pros
- ✔ Lots of flexibility.
- ✔ Easy way to add a single room.
Cons
- ✖ Not the cheapest option.
- ✖ Reduces outdoor/garden space.
Single-Storey Wraparound Extension Cost
A wraparound extension is the combination of a rear and side extension. This is the style that homeowners tend to go with when they want to add a large amount of space to the ground floor of their property.
The average single-storey wraparound extension cost in the UK is between £50,000 and £100,000, and around £1,950 per m².
Pros
- ✔ Creates a lot of extra living space.
- ✔ Provides a lot of options.
Cons
- ✖ Much more expensive than a side extension.
- ✖ You're more likely to need planning permission as the design will often exceed permitted development limits.
Single-Storey Kitchen Extension Cost
Many homeowners who build a single-storey extension in the UK do so to expand and remodel the kitchen. They're used to increase the working area in a kitchen, but are also frequently designed to open up more dining and living space.
The average kitchen extension cost in the UK is £50,000, or £1,850 per m², but the price can extend well beyond this depending on the size of the extension and the quality of the materials used.
Pros
- ✔ Can get a kitchen to suit your needs perfectly.
- ✔ Facilitates open-plan kitchen and dining rooms.
Cons
- ✖ Can be expensive to replace a kitchen.
- ✖ Leaves you without a working kitchen throughout the duration of the build.
Other Types of Single-Storey Extensions
Side, rear, wraparound, and kitchen single-storey extensions are common types of ground-level extensions.
However, there are three other options which you could explore:
- Timber Frame Extensions — An alternative to using a traditional extension, it's favoured by some people as the prefabricated frames make it quicker and easier to complete the extension. The average single-storey timber frame extension cost is £36,000.
- Flat Pack Extensions — This involves using a collection of prefabricated flat pack materials to assemble a house extension. You can complete a flat pack extension more quickly, but there is more limited customisation available. The average single-storey flat pack extension cost is £25,000.
- Flat Roof Extensions — A type of extension where the roof is almost completely flat, which tends to cost less than a traditional extension. However, it requires regular maintenance to prevent issues from developing. The average single-storey flat roof extension cost is £50,000.
Labour Cost of a Single-Storey Extension
The labour costs and timescales will vary greatly depending on the exact work you need to have done in your extension.
The following sections should give you a rough estimate of typical costs and timescales involved.
Labour costs in London are likely to be 20% higher than in the rest of the UK.
Timescale and Labour Cost Based on Type of Extension
| Type of Extension | Duration | Average Labour Costs |
|---|---|---|
| Lean-to Rear | 11 to 13 weeks | £25,000–£40,000 |
| Side Return | 8 to 10 weeks | £8,000–£12,000 |
| Side Extension | 9 to 12 weeks | £15,000–£25,000 |
| Wraparound | 10 to 14 weeks | £40,000–£100,000 |
| Kitchen | 10 to 14 weeks | £25,000–£100,000 |
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Cost per Hour of Different Tradespeople
| Tradesperson | Average Cost Per Hour |
|---|---|
| Builder | £20–£35 |
| Tiler | £20–£40 |
| Plumber | £35–£45 |
| Electrician | £50–£80 |
| Plasterer | £30–£50 |
| Decorator | £20–£50 |
| Joiner | £35–£45 |
| Roofer | £30–£40 |
| Kitchen Fitter | £35–£50 |
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Supply Cost of a Single-Storey Extension
When calculating your extension costs, there are many materials to consider! It's easy to see how the price of a single-storey extension can add up quickly.
In this section, we cover the main material prices you need to know about.
Window Prices
Most single-storey extensions include between 2 and 4 windows, so you can expect to spend around £500 to £3,600 on windows depending on the size, style, and specification you choose, with Velux and uPVC being the most common options.
| Type | Size (cm) | Average Cost |
|---|---|---|
| Velux | 98 x 78 | £325–£375 |
| Velux | 140 x 78 | £400–£450 |
| Velux | 180 x 78 | £500–£550 |
| uPVC | 60 x 90 | £250–£400 |
| uPVC | 90 x 120 | £400–£600 |
| uPVC | 120 x 120 | £650–£900 |
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Door Prices
Most extensions require at least one external door, with total door costs typically ranging from £300 to £1,500, although large patio or bi-fold door systems can cost considerably more.
| Type | Average Cost |
|---|---|
| Internal | £50–£200 |
| External | £300–£500 |
| Patio | £300–£1,000 |
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Flooring Prices
For a typical 20m² extension, flooring materials usually cost between £100 and £1,400, depending on the type of flooring selected, not including labour for fitting the flooring.
| Type | Average Cost per m² |
|---|---|
| Vinyl | £5–£20 |
| Wood | £20–£70 |
| Carpet | £5–£40 |
| Tile | £10–£60 |
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Heating Prices
The total cost of heating for a single-storey extension is typically between £200 and £4,000, depending on whether you choose to have radiators, install underfloor heating, or choose to upgrade your boiler.
| Type of Heating | Average Cost |
|---|---|
| Traditional Radiator | £60–£150 |
| Electric Radiator | £150–£300 |
| Underfloor Heating | £100–£200 per m² |
| Boiler | £1,500–£2,500 |
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Kitchen Prices
A complete kitchen for a single-storey extension typically costs between £5,000 and £15,000 for units, worktops, and essential appliances, although premium kitchens can cost significantly more.
| Item | Average Cost |
|---|---|
| Units with Doors and Handles | £3,200–£5,500 |
| Work Surface | £200–£2,000 |
| Fridge | £400–£1,200 |
| Fridge-Freezer | £600–£800 |
| American Style Fridge | £500–£1,300 |
| Chest Freezer | £160–£500 |
| Gas Hob | £100–£500 |
| Induction Hob | £300–£900 |
| Ceramic Hob | £150–£300 |
| Single Oven | £500–£1,100 |
| Double Oven | £400–£1,200 |
| Dishwasher | £400–£1,000 |
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Bathroom Suite Prices
If your extension includes a bathroom, expect to pay around £390 to £2,950 for the main fixtures and fittings before installation costs are added.
| Fixture | Average Cost |
|---|---|
| Bath | £80–£500 |
| Shower | £60–£1,000 |
| Shower enclosure | £100–£550 |
| Toilet | £50–£500 |
| Sink | £50–£300 |
| Taps | £50–£100 |
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Lighting Prices
Most single-storey extensions require between 4 and 10 light fittings, with total lighting costs typically ranging from £200 to £1,000 depending on the style and number of fittings installed.
| Type of Lighting | Average Cost |
|---|---|
| Pendant/chandelier | £40–£100 |
| Simple ceiling or wall lamp | £40–£60 |
| Recessed spotlights | £80–£110 |
| Dimmable ceiling or wall lights | £80–£100 |
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Additional Single-Storey Extension Costs
Whenever you get work done on your home, there are things that you need, or problems that arise, that need to be taken into account. This is especially true if you need to have a building control inspection.
In this section, we cover some of the additional costs of a single-storey extension that you might not have considered.
Skip Hire Cost
Rubble and waste are created when you have an extension added to your home. The easiest way to dispose of this is by hiring a skip.
The average cost of a skip hire is between £250 and £450.
Keep in mind that you may require multiple skips, which will increase the amount of money you need to put aside just to handle waste removal.
Removing Drains Cost
If your existing drains are in the way of an extension you're planning, then you'll need to move them to a new location.
To check if this is required, you'll need to have a drain survey carried out. Drain survey prices are typically around £250.
If your drains do need to be relocated, then you can expect it to cost between £200 and £1,300.
We're planning an extension and there's a drain running near where the foundations would go. How close can foundations be built to an existing drain?
"You can build over the pipe with concrete lintels, but you would normally need a build over agreement, which is normal.
If there is a manhole cover where the extension is going to be built, that would need to be moved so that there is still access."
If there is a manhole cover where the extension is going to be built, that would need to be moved so that there is still access."
Site Survey Cost
Before getting any major work done, it's advisable to have a site survey completed. This involves having a surveyor take a closer look at your property to identify any issues that already exist, or might arise during work.
The average cost of a house survey is between £600 and £1,400, varying depending on the size of your home. Although it's tempting to skip this to lower the total project cost, it can save money in the long run.
You will also have to ensure the site is clear before construction can begin, which may involve removing existing structures, plants, and other obstacles.
Architect Cost
It's not a legal requirement to hire an architect to plan the design of a single-storey extension in the UK, but many people find hiring one helpful to keep the project on task.
Architect prices are between 8% and 15% of the total cost of the extension you're looking to have.
Party Wall Agreement
In England and Wales, you must legally give your neighbour written notice if you will be working on a shared wall (e.g. on a semi-detached house), building on or at the boundary, or digging near their property's foundations. This should be done between 2 months and a year before the work starts, and they have 14 days to agree in writing.
If they don't consent or you don't hear back, you will need a surveyor to draw up a Party Wall Agreement. The average cost of obtaining one ranges from £700 to £2,000, but if your neighbour provides written consent, there will be no cost.
Structural Engineer
Structural engineers are often required to assess the structural integrity of your property and the proposed extension. They provide detailed reports and calculations that may be necessary for planning applications or building regulations.
The typical cost of hiring a structural engineer to draw up structural designs for a single-storey extension is between £400 and £2,000.
Temporary Accommodation
You may need to find temporary accommodation if your extension is being built while you are still living in the property. While not a requirement, certain parts of the build can be noisy and disruptive, so it's worth considering this option.
Existing Extension Removal
The costs for building a new single-storey extension are typically based on having clear ground for your new extension to be built on, but if you are replacing an existing extension, there will be additional costs to demolish and remove this first.
Check if your builder includes this in their quote, but if they don't, the average cost to demolish an old extension is between £3,000 and £5,000 in the UK, but this will depend on the type of extension that you're looking to demolish.
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What Impacts the Cost of a Single-Storey Extension?
There are a few factors to bear in mind when you are setting a budget for a single-storey extension.
The two main factors that affect the cost of a single-storey extension are the size and the finish. But there are other factors that it is worth keeping in mind when you are making your plans.
Size of the Extension
The single biggest factor that will impact the cost of a single-storey extension is the size of it. The bigger the extension is, the more you will end up paying.
If the area inside the extension is simple, with no internal walls, this will slightly lower the cost of a single-storey extension per m². But even with this in mind, larger single-storey extensions will require you to set aside more money.
Quality of Fixtures and Fittings
The next biggest factor impacting the cost of a single-storey extension is the quality of the finish. Choosing high-end options can lead to the final price being more than double what it would be when choosing more basic-level materials.
Fitting premium hardwood flooring, skylight windows, bi-folding doors, and high-end fixtures and furnishings will increase costs compared to choosing more budget-friendly materials.
Type of Extension
The type of extension you choose will go a long way towards dictating how large your extension will be.
Side return extensions create the smallest extra living space, so they tend to be the cheapest type of single-storey extension.
On the other hand, a wraparound kitchen extension will create the most space and likely include the most costly fittings and fixtures, so it will be a more costly option.
Groundworks Required
If digging the foundations and laying the footing for your single-storey extension proves to be difficult, then the cost will increase. This might be the case if the ground is hard to work with. Debris in the ground can also raise the costs, as can rerouting utilities.
Difficult structural work can also add to the overall cost of your extension, for example, removing load-bearing walls from the existing property.
Purpose of the Extension
The purpose of your extension will also play a role in determining the overall cost. For example, if you're planning to use the extension as a home office or a gym, you may need to invest in higher-quality materials and more sophisticated fixtures.
Installing a bathroom or a kitchen will also increase the overall cost, sometimes significantly, compared to creating a simple living space or bedroom.
Location
Where your property is located can also affect the cost of your extension. In areas where labour and materials are more expensive, such as London or the South East, the overall cost will be higher.
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Single-Storey Extension Roof Costs
When you get a single-storey extension, you have a few main roofing options to consider. What option you decide to go with will depend on the aesthetic you want and your budget.
Pitched Roof Cost
A pitched roof allows water to run off and will fit in with the look and feel of the rest of your home. You'll have a range of pitches to choose from, and Velux windows can be incorporated if you want to maximise the amount of light entering your property.
The average cost of a pitched roof is between £9,000 and £15,000.
Pros
- ✔ Loft space can be used for storage.
- ✔ Long-lasting.
Cons
- ✖ Not cheap.
- ✖ More likely to require planning permission if the height exceeds the limit for permitted development.
Flat Roof Cost
A flat roof is an affordable and easy-to-install option, which makes it a good choice for single-storey extensions.
The average cost of a flat roof is between £5,000 and £8,000.
Pros
- ✔ Affordable.
- ✔ Easy to install.
Cons
- ✖ Lifespan varies depending on the membrane used and quality of fitting.
- ✖ Commonly collects water and can be prone to leaks/water pooling.
Glazed Roof Cost
Glazed roofs are ideal for letting more light into side extensions. They typically cost around £1,000 per panel.
For a medium-sized extension that requires multiple panels, you'd be looking at a total cost of between £6,000 and £12,000.
Pros
- ✔ Natural light.
- ✔ Striking design feature.
Cons
- ✖ Expensive.
- ✖ Poor insulation.
Green Roof Cost
Green roofs are quite recognisable, as they have plants, usually sedum or wildflower mats, growing on top of them.
They are an environmentally sound option and also provide excellent insulation.
The average cost of a green roof is £100 to £140 per m². For an average single-storey extension, this is around £6,500 to £9,000.
Pros
- ✔ Excellent insulation.
- ✔ Environmentally friendly.
Cons
- ✖ Expensive to install.
- ✖ Ongoing maintenance required.
Benefits of a Single-Storey Extension
There are several reasons to consider adding an extension to your home, including the following:
- More Storage Space — Building an extension gives you the opportunity to add storage that perfectly suits your needs. You can ensure you have the perfect space for anything that is currently cluttering up your living spaces.
- Extra Living Space — An extension provides you with more space to spread out in your home. For growing families, this can relieve issues and make home life more enjoyable.
- Modernise Your Home — Adding an extension is an opportunity to change the look and feel of your home. You could rearrange the floor plan and align it with your needs and wants. Especially if you have an older property, adding a single-storey extension is an excellent way to update the space and make it more modern.
- Energy Efficiency — Modern designs can be very energy efficient. By using sustainable materials and technologies, you can make your property more efficient, which can reduce energy bills and increase your property's appeal to potential buyers in the future.
- Faster Build — Compared to two-storey extensions, ground floor extensions are quick to build, meaning less disruption and lower costs.
- Enhanced Natural Light — By sticking to one storey, you can keep natural light entering the upper floors of your property. Extensions often use large bi-fold doors to maximise natural light in the new space.
Building Regulations & Planning Permission for a Single-Storey Extension
Before you start work on your single-storey extension, it's a good idea to understand what permission or approval you might need for your project.
Single-Storey Extensions & Building Regulations
Any building work done on a home that makes major changes, like a single-storey extension, needs to comply with the local authority's building regulations, and Building Control fees vary depending on the size and complexity of your extension:
- Full Plans Application — Good for larger, complex extensions, requiring a lot of detail upfront. This costs between £250 and £550.
- Building Notice — Best for small and simple projects, with less detail needed upfront. This costs between £450 and £900.
It's good to note: These are just Building Control's costs which cover the application and inspections. While Full Plans might seem like the cheaper option, the more detailed drawings you will need to submit could mean spending £1,000 or more in professional fees.
Planning Permission for Single-Storey Extensions
In England, many single-storey extensions can be built without planning permission under permitted development rights. Rules vary in other parts of the UK, so it's always worth checking whether you need planning permission with your local council.
To build your single-storey extension using standard permitted development rights, it will need to meet the following criteria:
- The property must be a full house (i.e. not a flat), and not listed or in an area with restrictions on development.
- The extension cannot be on the front of the property.
- A single-storey extension on a detached property can extend up to 4 metres to the rear. The limit for all other houses is 3 metres.
- The maximum height is 4 metres.
- If the extension is within 2 metres of the property boundary, the eaves height must not be more than 3 metres.
- Any extension should be of the same or similar material as the existing property.
- No more than half of the land around the original house will be covered by the new extension and any other sheds or outbuildings combined (anything previous owners built counts too).
- A side extension can be no more than half the width of the original home and must be on a side not facing a highway.
A larger single-storey extension might be allowed under the prior approval scheme for larger home extensions, also known as the Neighbour Consultation Scheme, which can allow rear single-storey extensions up to 8m for detached properties, and 6m for all other property types.
Your project will need to meet the other applicable standard permitted development requirements listed above, and you will also need to apply to the local planning authority for prior approval before you start work, so they can check your project meets necessary requirements and assess the extension's impact on your neighbours.
The cost of applying for prior approval permitted development is £249 in England. The work can go ahead when you either get approval, the council says it isn't needed, or you don't hear back after 42 days.
I've heard some extensions don't need planning permission, but I'm confused about how much you're actually allowed to build. What are the usual limits?
"Single storey extension to rear is 3m for an attached property, 4m for a detached property.
Single storey to the side up to half the width of your existing house.
Further information is available on the Planning Portal website."
Single storey to the side up to half the width of your existing house.
Further information is available on the Planning Portal website."
Applying for Planning Permission
A lot of extensions will be covered under the standard and prior approval permitted development rules outlined above. If yours isn't, you will need to apply for planning permission.
If you're unsure, most councils offer a consultation service to help you check and to provide advice on submitting an application. This typically costs between £50 and £250, with an average of around £150.
If you need planning permission, you can apply through your local council's website or via the Online Planning Portal. You can make the application yourself or ask your architect or designer to submit it for you.
In England, applying for planning permission for an extension to an existing dwelling currently costs £548. Fees vary in other parts of the UK. Once your application is submitted it typically takes around 8 weeks for a decision.
When is the best time to build an extension? Is there a better season to start or does it not really matter in practice?
"In practice it doesn't matter that much, starting in the middle of winter can bring up some challenges, the shorter days can prolong a project. Apart from that you will be good to start any time!"
What's Involved in Building a Single-Storey Extension?
Even the smallest single-storey extension can be a challenging construction project, and unless you are a professional builder, you are unlikely to be able to complete the whole job on your own.
It's a good idea to get a number of quotes to make sure you get the best price and find the right tradesperson, and with MyJobQuote you can get fast, free, no-obligation quotes from builders near you.
Here's an overview of what you can expect when you hire a professional to complete your single-storey extension.
Before the Build Starts
- Initial Visit & Survey — Your chosen contractor will visit your property to discuss what you're looking to achieve, take the necessary measurements, check access, and assess the site to identify any potential challenges early on.
- Plans, Permissions & Building Control — You'll need to submit drawings and a notice of intent to start work to Building Control. You will also need to make sure you have the necessary planning permission or prior approval, unless you've confirmed the work can go ahead as permitted development.
- Site Setup — Before the work begins, your builder will prepare the site. This may include organising access, clearing the area for materials, getting skips delivered, and setting up barriers and safety equipment so they can start work.
During the Build
- Groundworks & Structural Build — Foundations are excavated and poured, drainage connections completed, and the damp-proof course and concrete floor slab are installed. The external walls are then built and tied into the existing property.
- Shell Completion & First Fix — The roof structure is constructed and covered, and windows and external doors are fitted to make the extension watertight. Once secure, first-fix electrics and plumbing are installed, and the opening into the existing house is created with structural supports added.
- Internal Works & Finish — Internal stud walls, insulation, and plasterboarding are completed, followed by plastering and making good. The space is then ready for second-fix services, decoration, and final finishes.
After the Build
- Second Fix & Finishing — Finishing touches such as sockets, switches, radiators, flooring, skirting, and internal doors are installed. If your extension includes a kitchen or bathroom, units, appliances, sanitaryware, and taps will also be fitted at this stage.
- Snagging & Clean-Up — A final inspection with your builder identifies any minor issues or "snags", which they will put right. Once complete, the site is cleared, tidied, and cleaned.
- Building Control Sign-Off — The final inspection from Building Control confirms that all work has been carried out to the required standard, and, once approved, you will receive a completion certificate. You will also receive certificates from the installer for any self-certified work such as electrical or plumbing work. Your extension is now ready for use or for you to apply the final decorative touches.
Single-Storey Extension Alternatives
If you're looking to increase the amount of floor space in your home, a single-storey extension is not the only option you have.
In this section, we go through a few other options you might want to consider.
Prefab Extension Cost
Prefab extensions (also known now as modular extensions) involve buying sections that are all manufactured elsewhere (i.e. prefabricated). These sections are then assembled and moved into position on your property using cranes.
One of the main advantages of a prefab extension is that it requires significantly less time to complete. However, a modular extension cannot be customised as much as a normal single-storey extension.
The average cost of a prefab extension in the UK is around £2,000 per m².
Pros
- ✔ Minimal disruption.
- ✔ Quick installation.
Cons
- ✖ Limited options.
- ✖ High cost per m².
Conservatory Cost
A conservatory is traditionally a mix of glass and brickwork. When it comes to selling your home, it's not considered a liveable indoor space. This means that it adds significantly less value to your home than some kind of extension. There are also limits on the services you can put in a conservatory.
The average conservatory cost in the UK is around £15,000. However, there are lower-cost conservatory designs that are more affordable. The average cost of a lean-to conservatory in the UK is around £8,250.
Pros
- ✔ Quick and easy to build.
- ✔ Affordable options.
Cons
- ✖ Hard to moderate the temperature.
- ✖ Less practical than a single-storey extension.
Glass Room Cost
Glass rooms are like conservatories, but without the brickwork. The glass panels also tend to be larger, giving them a more modern look.
The average cost of a glass room in the UK is between £15,000 and £70,000.
Pros
- ✔ Uninterrupted views.
- ✔ Modern, bespoke finish.
Cons
- ✖ Expensive to build.
- ✖ Can be costly to heat.
Orangery Cost
Before conservatories, there were orangeries. The main difference is that an orangery is mainly made of fully insulated bricks. Traditionally, the roof is flat and has a raised glass lantern window to allow in light.
The average cost of an orangery in the UK is about £22,000.
Pros
- ✔ Provides more space than a conservatory.
- ✔ Provides more light than a traditional extension.
Cons
- ✖ More expensive than a conservatory.
- ✖ The flat roof can require maintenance.
Loft Conversion Cost
Loft conversions involve turning your loft space into a habitable area. They're frequently used to add bedrooms, bathrooms, and offices to a home. The main advantage of a loft conversion over a single-storey extension is that it doesn't sacrifice your outdoor space (i.e. the garden).
The average cost of a loft conversion in the UK is around £40,000. However, a small basic loft conversion that converts about 13m² worth of space (one room) will usually cost between £19,500 and £29,500.
Pros
- ✔ No need to sacrifice outdoor space.
- ✔ Provides a good return on investment.
Cons
- ✖ Requires sacrificing some internal space for a staircase.
- ✖ Can be expensive to make a usable space.
Checklist: Hiring a Single-Storey Extension Builder in the UK
The contractor you hire for the extension will also likely handle all the project management. This is an important role, as many people need to be coordinated to keep things rolling along.
Here are some things to look out for:
- Are they happy to offer you an itemised cost breakdown? They should be able to give you a breakdown of the expected costs of a single-storey extension.
- Have they got proof of completed single-storey extension projects? Ask to see examples of previous work they have completed.
- Can you look at their past customer reviews? Reading what previous clients have said about their single-storey extensions will give you a good idea of the trader's workmanship.
- Who is responsible for organising building control visits? Most contractors will do this on your behalf, but make sure it's clearly agreed, as this is ultimately the homeowner's responsibility.
- Are the builders part of any trade associations? Check if they are members of a trade association like the Federation of Master Builders. This is not a guarantee of quality, but nevertheless a good sign.
- Have they got insurance? Make sure there is public liability insurance as a minimum.
I'm considering doing the internal work myself with some of my extended family to keep costs down. What would be included in the shell extension? Is this something that builders are happy to do, or will they just not bother quoting for a partial job?
"Yes, a lot of builders will consider just doing the shell build of an extension. I would include all groundworks and brick and blockwork that is required to take it to roof level, then fully roofed. Depending on the customer, also supply and fit the windows and doors so the extension is watertight."
FAQs
How Close to Property Boundaries Can You Build a Single-Storey Extension?
Under England's permitted development rules, there is no limit on how close an extension can be to a boundary, but you must give your neighbour written notice if the extension will be built right up to or on the boundary. If the extension is within 2 metres of a boundary, its eaves can't be higher than 3 metres.
Can I Build a Single-Storey Extension Myself?
Anything structural should be left to the professionals, and you will likely need to hire an electrician or plumber to deal with jobs that need certification to comply with the relevant regulations. If you want to do some of the work to help keep costs down, you could take on straightforward tasks like flooring, hanging doors, or decorating, but make sure you agree on this all with your contractor, so they can plan the work around you.
Where Can You Get Single-Storey Extension Ideas?
There are lots of interesting home extension ideas from which you can draw inspiration to create the perfect space for you and your family. It can also be rewarding to speak with people that you know who have built a single-storey extension.
How Much Does a 3m by 4m House Extension Cost?
A 3 metre house extension (around 12m²) will cost between £15,000 and £33,000, depending on finish and quality of materials used.
What Is the Cheapest Way to Extend a House?
The fewer structural changes you make (moving walls, or relocating drains), the lower your overall single-storey extension cost will be, helping you to make cost-effective decisions. Opting for standard materials instead of luxury materials and other upgrades will also keep your costs low, helping you to stay within budget. The cheapest option is usually a flat roof rear extension.
Is a 3m Extension Worth It?
A 3m extension is often a worthwhile investment, providing additional living space such as an open-plan kitchen-diner or living space with less hassle than moving house. Extensions 3m beyond the original back wall also usually fall under permitted development rights in England, provided they meet the other criteria.
Will Building a Single-Storey Extension Increase My Home Value?
In an October 2025 report from Nationwide, it's highlighted that extensions or loft conversions with a large double bedroom and a bathroom can increase the value of a 3-bed, 1-bath house by up to 24%.
Actual gains depend on the type and size of your extension, the build quality, and your location in the UK.
Do I Need to Hire an Architect for a Single-Storey Extension?
While an architect isn't necessary for a lot of single-storey extensions, and an experienced builder could be happy to work without one, architectural plans may prove useful for larger or complicated projects.
If you have a set of plans to follow, it means that there is a pre-agreed vision for what the final look of your extension will be. This could save money in the long run, as it will reduce any issues that can arise from miscommunication and the number of last-minute changes you make.
